1. Field of the Invention
The invention relates to methods and apparatus for electrical resection of tissue.
2. Endoscopic Tissue Resection
Surgical tissue resection deep within body cavities may be performed either under direct vision or endoscopically with the aid of electrodes which are elongated (along a longitudinal axis) and thin enough to be inserted directly into the incision or placed through an endoscope. Notwithstanding their relatively small transverse dimensions, these electrodes comprise at least one insulated electrical conductor and commonly have two. Monopolar electrodes, which in use rely on a return current path through the patient's body, may have only one or a plurality of insulated electrical conductors. Bipolar electrodes, in contrast, provide a return current path through one or more insulated electrical conductors; hence bipolar electrodes commonly have two insulated conductors. Electrodes preferably additionally comprise an electrically energized electrode cutting loop tip (generally a wire which may be straight or bent into a curved, circular or oval shape). Electrodes having two insulated conductors, which may be either monopolar or bipolar, typically have cutting loops made of a length of wire bent into an open circular or oval loop shape and coupled to the conductors, one end of the wire loop coupled to each conductor.
Designed to be manipulated from outside a patient's body through a relatively small orifice or incision, an electrode cutting tip intended for endoscopic surgery may deflect significantly under the influence of relatively small lateral (bending) forces substantially perpendicular to the electrode's longitudinal axis or torsional (twisting) forces which act around the electrode's longitudinal axis. The surgeon counteracts any unintended deflections and otherwise guides the tip along a desired cutting plane by applying corrective forces while viewing the cutting tip movement through the endoscope.
Precise guidance of an electrode cutting tip along a predetermined cutting plane requires exceptional skill because of the restricted visibility offered by an endoscope and the relatively great distances separating the surgeon's hands from the tissue being rescctcd. This is particularly true during electrical tissue resection because relatively small forces are sufficient to alter the path of an electrode cutting tip cutting through tissue. Such small forces, acting on the cutting tip at a point substantially distant from the surgeon's hand, are difficult for the surgeon to sense.
Adding to the difficulty of controlling movement of electrode cutting tips is the variety of forms the cutting tips may take, the type of tissue through which they are cutting, and the tip position with respect to existing tissue planes. An electrode cutting tip with self-guiding characteristics would tend to reduce both the incidence and range of erratic tip movement and also reduce the demands on the surgeon for guiding and correcting electrode movement. Such a self-guiding electrode would be particularly useful in surgical resection of tissue within the uterus, a roughly triangular organ in which portions of internal tissue surfaces lie in substantially parallel planes and comprise relatively uniform layers of substantially homogeneous tissue.
Greater accuracy in positioning the electrode cutting tip, in turn, would tend to reduce the time required for a variety of endoscopic surgical procedures while simultaneously increasing treatment efficacy. Reductions in cost and the likelihood of post-operative complications would naturally follow. Depending on the surgical site, electrode configuration, and tissues to be resected, various construction features related to self-guiding functions would be desirable.